PTA Hardfacing
Arcraft Plasma
India
PTA Hardfacing
• The Plasma Transferred Arc
Process ( PTA ) has been in
use since 1962 for surfacing
of parts .
• The applications possible
with PTA are hardfacing to
protect against extreme
conditions in service life like
heat , abrasion , corrosion ,
erosion ,adhesive and
abrasive wear etc.
• It is also use to recondition
worn out parts or build up
of mis machined parts.
PLASMA
• Plasma is a state of matter resulting from the inonisation of
gas. It is composed of positive ions and free negative
electrons. Its ionized condition enables it to conduct current.
• Transformation of gas into plasma requires energy and the
ionization level increases according to temperature ranging
from 6000 to 20000 degrees centigrade. Since the pressure
approximates to that of the atmosphere the impact of the fast
moving particles on one another are numerous enough for
the transformation of their kinetic energy into heat to result
in a considerable rise in temperature.
Plasma Torch
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The arc is struck between the
Tungsten electrode (Cathode) and
the job which is the anode . The fine
bore copper nozzle constricts the arc
into a fine beam as compared to the
open arc of TIG welding.
Powder is fed by a powder feeder
into the plasma arc through specially
drilled holes in the copper nozzle .
Torches using external wire feed are
also available . It is possible to use
both powder and wire feed
combination if extra ordinary high
deposit rates are required.
Process
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Although many consider Plasma Transferred Arc System (PTA) as a Thermal spray
process it is a high energy, inert gas welding process rather than a spraying process.
PTA deposition is also called PTAW surfacing because the American Welding Society
classifies the PTA deposition under Plasma Welding category .
Argon is basically used for arc plasma supply, powder transport and molten material
shielding. The coating material is fed into the Plasma arc in either powder or wire
form. The plasma torch has to be held at a distance of 3 to 8 mm from the
workpiece mostly in 1 G position.
PTA results in a metallurgical bond with a bond strength of 65000 psi while a
average NTA ( Non Transferred Arc ) deposit would feature about 6500 psi . This is
because PTA deposits are welded on the substrate.
PTA is suitable for manual, semi or fully automatic operations using manipulators,
positioners , oscillators and micro processor controls . It can be used with Robots
and adapted with CNC systems. It produces a very high quality deposit offering
optimal protection with minimal dilution or deformation of the base material which
are relatively low cost surfaces in the case of Hardfacing .
Types of Systems Available
• Automated PTA systems
• The Main power source
itself consist of two power
sources for the pilot arc and
main transferred arc , Arc
starting system , Gas
Flowmeters for plasma and
shielding gas , Plumbing
board for torch connections
, Switches and failure
indicators .
PTA with powder welding for internal diameters
• PTA can deposit a coating
on an internal or external
surface of a cylinder.
Internal diameters as small
as 2″ (45mm plus) can be
hardfaced with no upper
limit .
• The max current capacity is
200 Amps DC for the ID
torch .
ID hardfacing with PTA
Manual or Automated Applications
• Manual Plasma torches • Arcraft designs and
are available upto 150
manufactures SPM as
Amps DC . Manual
per the jobs and
plasma torches and
customer requirements.
portable power sources • The designs can be semi
are ideal for repair
automatic or fully
shops and site
automatic.
applications .
• We use PLC , micro
processor or CNC
technology for control
of the system.
SPM for engine valves
Hardfacing with SPM
Plug valve / Ship Engine valve /mechanical seals
Advantages of P.T.A.
• An attractive controlled weld bead reducing cost / wastage
of consumables with little or no ripple reducing time and
cost of post weld machining .
• Very low dilution with the base metal .
• High, density bead without porosity , oxidation &
inclusions..
• Highly automated
• High powder utilisation
• Very wide range of hardfacing materials
Versatility in applications
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Wide range of deposits: The PTA- applied deposits can be as thin as only 0.5 mm or as thick as 50 or 60 mm.
In fact there is no ‘upper’ limit since the thickness may easily be built up to any desired level by repetition
i.e. use of ‘multiple passes’.
Wide range of materials: The substrate to be coated may be any industrial metal or alloy. Even difficult
materials HCHC alloys, die steels, hot-die steels, HSS etc can be easily coated with a wide variety of
materials.
Wide range of coating materials: The coating materials may be elemental metals from aluminium upto
zirconium (only solids), or their alloys , cermets e.g. nickel-aluminide, tungsten carbide mixed with ferrous
or non ferrous metal powder. A wide range of proprietory overlay alloys are available for practically any
part. Some alloys are very hard; others are softer with hard abrasion-resistant particles dispersed in a
matrix. Certain alloys are made to rebuild a part to a required dimension while others are designed to be a
final overlay that protects the work surface. Soft alloys, medium and high hardness materials, and carbide
composites can be deposited on a variety of substrates to achieve diverse properties such as mechanical
strength, wear and corrosion resistance, and creep
Narrow range of parameters: As compared to the more famous and established NTA (non transfer arc)
option the PTA variation offers a smaller number of parameters to be controlled. The main parameters are
arc current, arc voltage (indirectly controlled by arc length), plasma gas flow , shield gas flow , carrier gas
flow rate and welding speed. Controlling these requires no special skills and an average welder can
confidently yield good deposits. In automated welding the parameters of speed of job movement and
speed of oscillation of torch are added.
Adaptability: The PTA option is basically simpler, and hence easy to be adapted for semi-or –fully automatic
manipulators or programmable electronic or computerized devices.
Heavy deposition: It is possible to increase the high deposition rates of the PTA deposition even further
than 10 kgs/Hr. For instance wire feeders can be used in conjunction with the powder feeder, stepping up
the deposition rate from as little as one kilogram/ minute upto several Kgs/mm.
Areas of Applications
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The PTA deposition or Surfacing process is one of the most versatile and useful techniques
used for what are generally referred as surfacing or overlaying processes.
Following are a few applications to which PTA Deposition has been applied successfully on
an international scale .
Hardfacing: Most of the industrial components in an enormous range of wear applications
benefit from application of a hand overlay. A variety of nickel-base alloys are available for
specific hardness, or a number of other properties combined.
Salvaging/Reclamation: An amazing bulk of all types of industrial components made from
simple or complex alloys (e.g. nickel-chromium alloys) are now being dumped as scrap. PTA
deposition offers reliable method for salvaging and reclamation .
Application of Special Materials: Sometimes it is a must to apply an overlay deposit of
special materials e.g. molybdenum or tungsten etc for lending resistance to elevated
temperatures (these are ‘refractory’ materials).. or in the case of industrial valves Stellite
equivalent for impact resistance .
Minute Repairs: There are sometimes defects in parts made from difficult-to-weld-materials
which cause them to be scrapped. The PTA deposition process can easily build up the
missing portion. Such defects are cracks, notches, dents, cavities, deep scratches or scoring
marks etc.
Thank you ! Do contact with your
requirements .
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Arcraft Plasma Equipments ( I ) Pvt Ltd
124 Diamond Industrial Estate ,
Ketkipada , Dahisar ( East )
Mumbai 400068 ,
India .
Phone - 00 91 22 - 28963247 , 28965890 , 28965745
Fax - 00 91 22 - 28966418
Sales Handphone - 00 91 - 9820684001
email : arcraftplasma@gmail.com
web : www.arcraftplasma.com